The goal of these experiments is to investigate the mechanisms of actions of halothane, isoflurane, desflurane and sevoflurane on the sarcolemma of atrial and ventricular cells, and to examine the interaction between these anesthetics and Ca2+ antagonists, adrenergic and cholinergic agonists. Determination of these interactions at the level of sarcolemmal signal transduction can help identify those processes whose alteration may be responsible for cardiac actions of these anesthetics. Comparisons of the voltage-gated and G protein-coupled ion channel activity will be achieved by measuring Na+, K+ and Ca2+ channel currents using voltage-clamp and patch-clamp methods on individual cardiac cells of the guinea pig. Specific objectives are: 1) To determine the mechanisms responsible for the effects of inhalation anesthetics on atrial and ventricular action potential characteristics by direct measurement of their actions on sarcolemmal voltage-sensitive Na+, Ca2+ and K+ currents, and to determine the interaction between inhalation anesthetics and Ca2+ antagonists on Ca2+ current. This is an extension of the current work by the principal investigator is coordinated as a major effort to understand the mechanisms by which inhalation anesthetics and related drugs modulate ionic fluxes across the sarcolemma of the cardiac muscle cells. 2) To examine how anesthetics alter the G protein-mediated regulation of adenylyl cyclase (AC) in intact atrial and ventricular cells by adrenergic agonists. The receptor-mediated cascade of signal transduction will be selectively stimulated or inhibited at the specific component including: a) receptor stimulation, b) direct G-protein activation, c) AC activation, d) protein kinase inhibition, e) second messenger measurements, or f) channel phosphorylation inhibition. 3) To examine how anesthetics alter the G protein-mediated regulation of K+ channel in intact atrial cells by cholinergic agonists. We will examine one of the best examples of a membrane-delimited (direct) coupling between receptor, G-protein and ionic channel, a coupling between the muscarinic cholinergic atrial receptor, GK protein and GK-gated ACh sensitive atrial K+ channel. Our major achievement over the years has been the ability to perform electrophysiological studies of Ca2+, Na+ and K+ currents, single channel kinetics. Using these methods, we are able to examine which transsarcolemmal currents are involved in producing changes in action potential characteristics. We have already demonstrated that different currents may be unevenly altered in the presence of anesthetics and how anesthetics differently affect [Ca2+]i and electrophysiologic properties of cardiac cells in the presence of calcium antagonists and adrenergic and cholinergic receptor stimulation. The proposed studies of this application are coordinated as a major effort to understand the mechanisms by which anesthetics in combination with other drugs modulate cardiac electrophysiology.